Excretory Products and their Elimination Test -3

The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries.

A minute vessel of this network runs parallel to the Henle’s loop forming a ‘U’ shaped vasa recta. Vasa recta is absent or highly reduced in cortical nephrons.

On the medial margin of the kidney is concave region called the renal hilum. The renal hilum is the entrance to the renal sinus. Structures such as the renal veins, artery, nerves and lymphatic vessels are located in the renal hilum.

The excretory system in human consistsof a pair of kidneys, one pair of ureters, aurinary bladder and a urethra. Kidneys are reddish brown, bean shaped structures situated between the levels of last thoracic and third lumbarvertebra close to the dorsal inner wall of the abdominal cavity.

Bowman cup contains glomerular capillaries to filter the blood. Blood enters the glomerular capillaries through afferent arteriole and leaves through efferent arteriole.

The pH of urine under healthy conditions is slightly less than 7 so, slightly acidic in nature.

Glomerular filtrate contains glucose, inorganic salts and creatinine but it do not contain globulins protein.

Podocytes are cells in the Bowman's capsule in the kidneys that wrap around capillaries of the glomerulus. The Bowman's capsule filters the blood, retaining large molecules such as proteins while smaller molecules such as water, salts, and sugars are filtered as the first step in the formation of urine.

Distal Convoluted Tubule (DCT): Conditional reabsorption of Na⁺ and water takes place in this segment. DCT is also capable of reabsorption of HCO^3- and selective secretion of hydrogen and potassium ions and NH₃ to maintain the pH and sodium-potassium balance in blood.

• Insects are uricotelic meaning they excrete uric acid like birds and reptiles. It is a terrestrial adaptation and helps to conserve water. 
• Aquatic animals like fishes excrete ammonia because ammonia requires a lot of water to dissolve. They are called ammonotelic. 
• Mammals are ureotelic, they excrete urea. 
• Some mollusc animals excrete amino acids and are also ammonotelic. 
• Thus, the correct answer is option D.

Blood enters the kidney via the renal artery, which forms many afferent arterioles, each of which delivers blood to an individual kidney nephron. The diameter of the afferent arteriole is greater than the diameter of the efferent arteriole. The pressure of the blood inside the glomerulus is increased due to the difference in diameter of the arterioles. This increased blood pressure helps to force the components of the blood out of the glomerular capillaries.

Correct Answer: A

The end products of aerobic metabolism of carbohydrates are carbon dioxide and water. Carbon dioxide remains dissolved in the blood and is carried by the veins to the lungs for oxygenation. If carbon dioxide is not removed from the metabolizing tissues, it will be toxic for that tissue and stop metabolism.

Animals that excrete excess nitrogen in the form of urea are ureotelic. Terrestrial animals cannot use water freely for excretion (because of less availability in the environment), so ammonia is converted into a less toxic and easily soluble product, urea. In mammals and semi-terrestrial adult amphibians, urea is a major nitrogenous excretory product, therefore these animals are called ureotelic.

The urinary system produces urine (nitrogenous water) and serves to excrete it to outside the body. Lymphatic system serves in fluid balance, fat absorption and defense. The circulatory system serves in exchange of nutrients and oxygen for waste and carbon dioxide respectively. Respiratory system serves to allow entry of oxygen from the air into blood and exit of carbon dioxide from blood to the air. The integumentary system covers the entire surface of the human body and serves as a barrier, site for waste elimination and temperature control. 

The blood is filtered through the nephrons in the kidney. The wastes from the blood is excreted from the renal tubules in the form of urine which is composed of water, salts, urea, uric acid, drugs, etc. This is the excretory product which is carried by the ureter to the urinary bladder and then removed out through the urethra.